Remediation　of　heavy-metal　contamination　by　biomineralization　has　become　an　environmentally　very　important　issue　in　the　last　two　decades.　Here　we　describe　the　transformation　of　amorphous　organo-Cr(III)　to　chromium　hydroxide　oxide　(guyanaite/grimaldiite)　by　hydrothermal　treatment　(HTT).　First,　glycine-Cr(III)　was　synthesized　to　serve　as　a　simple　model　for　exploring　the　conditions　favoring　HTT.　Cell-bound　Cr(III)　was　obtained　by　the　reduction　of　hexavalent　chromium　[Cr(VI)]　to　trivalent　chromium　[Cr(III)]　by　Bacillus　cereus.　Then　the　reduced　Cr(III)　was　chelated　by　ligands　at　the　cell　surface,　forming　cell-bound　Cr(III).　Subsequently,　HTT　was　applied　to　treat　cell-bound　Cr(III)　at　different　temperatures　and　for　different　lengths　of　time.　The　results　showed　that,　by　this　treatment　at　200°C　for　7 days　or　at　250°C　for　1 day,　glycine-Cr(III)　was　converted　to　trivalent　chromium　mineral　(guyanaite/grimaldiite),　having　the　form　of　nanosheets　with　a　length　of　10∼20 nm　and　a　width　of　3∼5 nm　under　the　described　conditions.　Cell-bound　Cr(III)　could　also　be　converted　to　guyanaite/grimaldiite　at　250°C　for　9 days　if　it　was　bound　by　an　organic　compound　more　complex　than　glycine.　Our　finding　showed　that　organo-Cr(III)　could　be　transformed　into　minerals　by　an　appropriate　hydrothermal　process,　which　is　applicable　to　bioremediation　of　heavy-metal　pollution.　Our　findings　also　suggest　that　organo-Cr(III)　may　play　an　important　role in　the　biogeochemistry　of　chromium.　©　2016　Taylor　&　Francis　Group,　LLC.